Re: Phase adjust (critical cap values)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 12/29/00 1:40:30 AM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

> >
>  > Running with 135-270ufd caused the motor voltage to drop as soon as the
>  > Variac was moved off the stop. The phase did vary but only by about
>  > 5-degrees before it dropped sync due to the low voltage.

Brian, all,

Considering what Richie mentioned about the higher Q's of the
large motors, this may make the cap value even more critical 
for large motors than for small ones.  A cap that is just a little
too small may give almost no phase shifting, and one that is
a little too large, will give unacceptable amounts of reso-rise,
and self-braking upon shutdown.

I found that even for small motors, the best size cap was within
just a 2uF range or so for a 50uF cap, or within 4% or so.  For
the large motors, a 1% tolerance may be needed.  Maybe
some resistance can be added also, to try to de-Q the circuit
some.  We'll see what comes up as folks experiment.

John Freau